1. Technical Field
The present invention relates to a turn signal cancel device adapted to automatically return a turn lever, which has been turned to a left turn indicating position or to a right turn indicating position, to a neutral position according to the fact that a steering wheel is rotated in a direction opposite to the direction indicated by the turn lever.
2. Related Art
The configuration of a related turn signal cancel device of such a kind is described hereinafter with reference to FIGS. 8 to 12. As shown in FIGS. 8 and 9, a cancel cam 1 is a cylindrically shaped member, which has a cancel convex portion la on the outer peripheral portion thereof, and adapted to be integrally rotated with a steering wheel (not shown).
A rectangular box body 2 having opening portions at both lateral end portions is provided in a fixed manner on the right side of this cancel cam 1. A bracket 3 is provided in the body 2 in such a way as to able to rotate around a shaft portion 3a. A base portion of a turn lever 4 is connected to the bracket 3. A moderation surface portion 5 having alternate formed ridge portions and valley portions is provided on the left-hand inner surface of the body 2. A moderation piece 6b is provided at the end portion of the bracket 3 and is pushed by a moderation spring 6a in a direction which the moderation piece 6b is press-contacted with the moderation portion 5. A moderation mechanism 7 includes the moderation surface portion 5, the moderation spring 6a, and the moderation piece 6b. 
The bracket 3 and the turn lever 4 are held selectively at a neutral position, a left turn indicating position (see FIG. 10) to which the turn lever 4 is turned therefrom in a direction of an arrow A1, and a right turn indicating position (not shown) to which the turn lever 4 is turned therefrom in a direction of an arrow A2 whose direction is opposite to the direction of the arrow A1, as illustrated in FIGS. 8 and 9. Incidentally, although not shown, a turn signal switch, whose contacts are switched according to the position of the bracket 3, is provided in the body 2.
A back plate 8 is nearly U-shaped as a whole, and includes pressed portions 8a and 8b at both end portions thereof. The back plate is attached onto a nearly central part of the top surface portion of the bracket 3 in such a manner as to be able to slide in the directions of arrows B1 and B2. A back-plate holding spring 9 for holding the back plate 8 at an intermediate position illustrated in FIG. 8 by a predetermined force is provided between the back plate 8 and the bracket 3. A cam portion 10 having a crest part is provided on a left-hand side portion of the top surface of the bracket 3.
A ratchet 11 is disposed in the top surface portion of the bracket 3. A shaft portion 11a is provided on the middle portion of the ratchet 11 so that the top end of the shaft portion 11a is inserted into a guide hole 12a, which is an elongated hole formed in a cover 12 (see FIG. 9) attached to the top surface portion of the body 2 in such a manner as to be able to move and rotate, and so that the bottom part of the shaft portion 11a moves along the cam portion 10. The ratchet 11 is pushed by a ratchet pushing spring 13 in a direction of an arrow C, that is, to the side of the cancel cam 1.
In a state in which the bracket 3 (thus, the turn lever 4) is placed at the neutral position illustrated in FIG. 8 in the aforementioned configuration, the bottom part of the shaft portion 11a of the ratchet 11 is placed at the top of the crest part of the cam portion 10. The ratchet 11 is held at a position where the leading end portion 11b thereof retreats from a rotational locus K (see the position indicated by a chain double-dashed line in FIG. 8) of a cancel convex portion 1a. 
When the turn lever 4 is turned from the neutral position thereof in the direction of, for instance, the arrow A1, and the bracket 3 is placed at the left turn indicating position illustrated in FIG. 10, the ratchet 11 is caused by the pushing force of the ratchet pushing spring 13 to frontwardly move in the direction of the arrow C during the bottom part of the shaft portion 11a moves along a slope of the cam portion 10. Then, the ratchet 11 is put into a state in which the leading end portion 11b thereof moves inside the rotational lotus K of the cancel convex portion 1a. 
When the cancel cam 1 is turned in the direction of the arrow D1 opposed to the indicated direction of the bracket 3 by the steering wheel during this state, the leading end portion 11b of the ratchet 11 is pushed in the same direction, so that the ratchet 11 is turned around the shaft portion 11a in the direction of an arrow E, and that the rear end thereof pushes the pressed portion 8a of the back plate 8. In the case that this pushing force exceeds the holding force of the moderation mechanism 7, the bracket 3 (thus, the turn lever 4) is turned and returned to the neutral position.
In the case that a phenomenon of what is called a grabby brake occurs, for example, the turn lever 4 is held by a driver at the left turn indicating position when the cancel operation is performed, an excessive pushing force 8a, which exceeds the holding force of the back-plate holding spring 9, of the back plate 8 acts on the pressed portion 8a of the back plate 8 from the rear end portion of the ratchet 11. Then, as illustrated in FIG. 11, the back plate 8 moves in the direction of the arrow B1. This permits the cancel convex portion la to pass therethrough in the direction of an arrow D1. Consequently, the ratchet 11 and the back plate 8 are prevented from being damaged when the phenomena of grabby brakes occur.
Incidentally, although the aforementioned operation is performed when the bracket 3 (thus, the turn lever 4) is turned to the left turn indicating position, a similar operation is performed when the bracket 3 (thus, the turn lever 4) is turned to the right turn indicating position.
However, the related cancel device has the following problem. That is, let F1 denote a vector representing the pushing force transmitted from the ratchet 11 to the back plate 8 when the cancel operation is performed as illustrated in FIG. 10. In this case, a vector F2 representing the force acting on the back-plate holding spring 9 is established as illustrated in FIG. 10. A vector F3 is a vector representing a vertical reaction force transmitted from the back plate 8 to the ratchet 11. In this case, the direction of the vector F1 representing the pushing force transmitted from the back plate 8 to the ratchet 11 is close to the direction of expansion and contraction of the back-plate holding spring 9 (that is, the direction of the arrow B1 or B2, in which the back plate 8 moves). Thus, when the cancel operation is performed, the vector F2 acting on the back-plate holding spring 9 has a large magnitude and exerts a large influence on the back-plate holding spring 9.
Thus, even when the cancel operation is performed at the rotational speed of the steering wheel (or of the cancel cam) under ordinary driving conditions, the back plate 8 easily moves. Therefore, as illustrated in FIG. 12, an amount of movement of the back plate 8 increases with increase in the rotational speed of the cancel cam 1 (or of the steering wheel) Consequently, a cancel error (that is, even when the ratchet 11 is turned by the cancel convex portion la, the bracket 3 is not returned to the neutral position thereof) easily occurs.
The present invention is accomplished in view of such circumstances. Accordingly, an object of the present invention is to provide a turn signal cancel device, which has a function of avoiding occurrences of phenomena of grabby brakes in a turn lever, and which can prevent occurrences of cancel errors as much as possible.
To achieve the foregoing object, according to the present invention, there is provided a turn signal cancel device that includes:
a cancel cam having a cancel convex portion defining a rotational locus adapted to be rotated by a steering wheel;
a bracket rotatably mounted in close proximity of the cancel cam, and selected among a left turn indicating position, a neutral position, or a right turn indicating position, by operating a turn lever;
at least one pressed portion provided in the bracket;
a moderation mechanism which holds the bracket at the selected positions;
a ratchet body portion adapted to move frontward so that a leading end portion of the ratchet body portion is within the rotational locus of the cancel convex portion, when the bracket is placed at the left turn indicating position or the right turn indicating position, and the ratchet body portion adapted to be turned by the cancel convex portion when the cancel cam is rotated;
a ratchet movable portion provided in a rear part of the ratchet body portion, movable in forward and backward directions of the ratchet body portion, and rotatable with the ratchet body portion, wherein the ratchet movable portion is rotated together with the ratchet body portion and pushes the pressed portion to return the bracket to the neutral position when the ratchet movable portion is rotated in a direction opposite to a direction indicated by the bracket in a state in which the bracket is placed at the left turn indicating position or the right turn indicating position; and
a movable portion pushing spring provided between the ratchet movable portion and the ratchet body portion, wherein the movable portion pushing spring permits the ratchet movable portion to move frontward to allow the cancel convex portion to pass therethrough causing a turning force to act on the bracket through the pressed portion in a direction in which the bracket is returned to the neutral position.
With the aforementioned configuration, under ordinary conditions, in a state in which the bracket is placed at the left turn indicating position or the right turn indicating position, when the cancel cam is rotated in a direction opposite to the indicated direction, the ratchet body portion and the ratchet movable portion are turned by the cancel convex portion. Then, the ratchet movable portion pushes the pressed portion to thereby return the bracket to the neutral position. In contrast, at an occurrence of a phenomenon of what is called a grabby brake, in which the turn lever is fixed, the excessive pushing force acting from the ratchet movable portion to the pressed portion is relieved by forward movement of the ratchet movable portion, which is performed against the spring force of the movable portion pushing spring.
In this case, the direction of a vector representing a force transmitted from the ratchet movable portion to the pressed portion of the bracket differs by nearly 90 degrees from the direction of movement of the ratchet movable portion, which is caused so as to relieve an excessive pushing force to be made to act on the pressed portion, or from the direction of expansion and contraction of the movable portion pushing spring. Thus, when a cancel operation is performed, the magnitude of a vector representing a force acting on the movable portion pushing spring is relatively small. Consequently, this force exerts a small influence on the movable portion pushing spring. Therefore, when a cancel operation is performed at the rotation speed of the cancel cam (thus, the rotation speed of the steering wheel) under ordinary driving conditions, the ratchet movable portion is difficult to move. Thus, an occurrence of a cancel error is prevented as much as possible.
According to an embodiment of this turn signal cancel device of the present invention, the ratchet movable portion has a pair of first abutting contact portions adapted to abut against the pressed portion when the bracket is returned to the neutral position, and also has a second abutting contact portion, disposed between the pair of first abutting contact portions and adapted to the pressed portion when the ratchet movable portion frontwardly moves against a spring force of the movable portion pushing spring.
Consequently, when the degree of inclination of the ratchet movable portion with respect to the pressed portion is large, the abutting contact portion to be made to abut the pressed portion changes from each of the first abutting contact portions to the second abutting contact portion. Thus, an engaging area (that is, a region, on which the ratchet movable portion abuts) of the pressed portion can be secured in such a manner as not to have a large area.